treewide: sysupgrade: don't use $ARGV in platform_do_upgrade()

treewide: sysupgrade: don't use $ARGV in platform_do_upgrade()

stage2 passes image path to platform_do_upgrade() as an argument so it
can be simply accessed using $1

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit 8b4bc7abe073489a3595eeb2d81818852319c148)
[rmilecki: dropping ARGV without this change broke sysupgrade]
Fixes: 6ac62c4b6cae ("base-files: don't set ARGV and ARGC")